DEOXYRIBONUCLEIC ACID

DNA

O.L Lesson Objectives

At the end of this lesson you should be able to  1. Outline the simple structure of DNA – 2

strands and A,T,C, G complement2.Distinguish between coding and non coding

structures3.Describe the triplet base code4.Outline the structure of RNA – refer to Uracil

and complement to DNA5.Know the function of mRNA6.Discuss the replication of DNA

What is DNA

Hereditary material

Carries and passes on genetic information

It is a nucleic acid

Made up of nucleotides

The DNA Double Helix

Two parallel strands Each with a series of bases to the insideThe bases are directly opposite each otherThe bases link each other in pairsThese links form the steps of the ladder

The DNA Double Helix

Parallel StrandParallel Strand

BaseBase

Hydrogen bond- link

The Bases

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

The Base Pair Rule

The bases can occur in any sequence along a strand of DNA

But the sequence must be complimentary to the sequence on the other strand

The Base Pair Rule

Adenine can only join to Thymine A T

Guanine can only join to Cytosine

G C

http://www.zerobio.com/drag_gr9/DNA/dna.htm

Building DNA

Building DNA

http://learn.genetics.utah.edu/units/basics/builddna/

Learning Check

What does DNA stand for?Name the four bases in DNAWhich base complements Adenine?Which base compliments Guanine?

Non Coding DNA

Only about 3% of DNA is composed of genes

97% of DNA is non coding DNA or junk DNA

Coding DNA

The parts of DNA that contain information to make RNA or protein

Coding DNA in genes are called exons

Non Coding DNA

Do not contain critical information for the production of protein

They are now thought to play a role in gene expression

Non coding DNA within genes is called introns

Learning Check

Label a gene and a piece of non coding DNA in the following picture

RNA

Ribonucleic Acid

Operates with DNA to make proteins

Has Uracil instead of Thymine

Differences between DNA and RNA

DNA

Double strand

Sugar is deoxyribose

Has Thymine

Very long

Self replicating

Found only in the

nucleus

RNA

Single strand

Sugar is ribose

Has Uracil

Short molecule

Not self replicating

Found in nucleus and

cytoplasm

Similarities between DNA and RNA

Both are nucleic acids

Both contain adenine, guanine and cytosine

nucleotides

Operate together to produce specific proteins

Learning Check

1. What does RNA stand for?

2. What three bases do DNA and RNA have in

common?

3. What base does RNA have instead of

Thymine?

4. Where do you find both DNA and RNA?

5. Where else will you find RNA?

H.L Objectives

AT THE END OF THIS SECTION YOU SHOULD KNOW …. .

DNA STRUCTURE – DEOXYRIBOSE SUGAR, SUGAR, PHOSPHATE AND 4 NAMED

NITROGENOUS BASESNUCLEOTIDE STRUCTURE

SPECIFIC PURINE AND PYRAMIDINE COUPLES – COMPLEMENTARYBASE PAIRS

HYDROGEN BONDINGDOUBLE HELIX

NUCLEIC ACID STRUCTURE

Higher Level

Nucleotides

Nucleotides are carbon ring structures containing

nitrogen linked to a 5-carbon sugar (a ribose)5-carbon sugar is either a ribose or a deoxyriboseIn eukaryotic cells nucleic acids are either:

Deoxyribose nucleic acids (DNA)

Ribose nucleic acids (RNA)

OH

OCH2

Sugar

H

HH

A Nucleotide

OH

NH2

N

N NN

BaseP

O

OH

HO O

Phosphate

2’3’

4’

5’

1’

H+

-

Coding and Non Coding Parts

Non coding StructuresSugar – Phosphate

Coding StructuresBase Sequences

Purine Bases

Adenine and Guanine

Double ringed molecular structures

Known as Purine Bases

Pyrimidine Bases

Thymine and Cytosine

single ringed structures

Known as Pyrimidine bases

Pyrimidines

NH2

O

N

N NHN

Guanine

N

N

Adenine

N

N

NH2

N O

NH2

N O

NH2

NCytosine

Purines

Uracil(RNA)CH3

N ON

O

NH

N ON

O

NH

Thymine(DNA)

Base Numbers

Number of Purine Bases =

Number of Pyrimidine Bases

This led to the discovery of Base Pairing

NO

H

NO

N

NH Cytosine

H

O

NN

N

N

N

H

H

Guanine -+

+

+

-

-

Base PairingGuanine And Cytosine

Three Hydrogen Bonds

CH 3N

ON

ONH+

- ThymineN

NN

N

HN H

-

+Adenine

Base PairingAdenine And Thymine

Two Hydrogen Bonds

Base PairingGuanine And Thymine

CH3

NO

N

ON

H+

- Thymine

H

O

NN

N

N

N

H

H

Guanine +

+

-

The Watson - Crick Model Of DNA

3.4 nm1 nm

0.34 nm

Majorgroove

Minorgroove

A T

T AG C

C G

C GG C

T A

A T

G CT A

A TC G

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What have you learned

Can you ……………… 1. Outline the simple structure of DNA2.Name the four bases and the base pairs in

DNA3.Distinguish between coding and non coding

structures4.Define triplet base code5.Outline the structure of RNA6.Name the bases in RNA and know the

function of mRNA7.Discuss the replication of DNA

End